The present disclosure relates to a reactor assembly for processing substrates and more particularly, to a distribution system for flowing gases and/or reactants into and out of the reactor assembly.
In many semiconductor fabrication processes, process gas is introduced into a process chamber of a reactor assembly through a gas distributor. Plasma may be formed from the gas to etch features on the substrate, deposit layers of material on the substrate, and the like. Gaseous byproducts formed during processing are exhausted from the process chamber via an exhaust system. In etching processes, the uniformity of the shape and size of features across the substrate is affected by the distribution of gaseous species across the substrate, especially when the size and spacing of the etched features become smaller. Similarly, in deposition processes, the thickness and composition of the deposited layer can vary across the surface of the substrate depending upon the distribution of gaseous species across the surface of the substrate.
Axial flow reactor assemblies often fail to provide a uniform distribution of gas and/or reactive gaseous species across the substrate resulting in variations in the shape and size of the etched features, the thickness of the deposited layer, or the like. Axial flow reactor assemblies typically include axisymmetric gas inlets located above and coaxial to the substrate, i.e., directly above the substrate to be processed. Consequently, the gas and/or reactant flow is normal to the substrate surface creating a subsequent radial flow pattern that is generally transverse to the substrate surface. This can lead to flow anomalies and non-uniformity in exposure of the gas and/or reactant to the substrate surface as effluent from the process on the substrate surface combines with the incoming gas flow.
Gas distribution systems placed upstream of the substrate have been employed with process chambers in an attempt to minimize the non-uniformity. Gas distribution systems typically include the use of specialized plates that are difficult to predict analytically and are largely designed by trial and error experimental methods. For example, the use of special baffle plates have been employed and are typically positioned in close proximity to the gas inlet in an attempt to improve uniformity of gas and/or reactive species distribution at the substrate surface. However, one problem with the use of baffle plates and/or gas distribution plates disposed upstream from the substrate is the potential for reactive species recombination. The additional surfaces provided by these plates adjacent to the flow of process gases provide a large surface area that can contribute to reactive species recombination. The recombination of reactive species can decrease the overall efficiency of the process, thereby increasing process times and reducing throughput. To avoid reactive species recombination, the baffle plates and/or gas distribution plates disposed at or near the gas inlet require the use of special materials inert to the operating environment such as quartz, alumina, other ceramics, specialized aluminum alloys with non-reactive coatings such as hard anodization, and the like. The use of these materials adds to the overall costs and complexity of the reactor assembly. Moreover, some special alloys such as aluminum based alloys typically use special cooling modifications incorporated within the baffle plate itself or added as an additional device to prevent heating of the baffle plate, gas distribution plate by the substrate, and/or the high temperature plasma gas. The heating of the baffle plate can cause loss of substrate temperature control within the process chamber as each subsequent substrate is now heated by the energy contained within the baffle plate and not by the chamber heating device, i.e., lamp array, heated chuck, or the like. The use of the baffle plate and/or gas distribution plate also increases the internal volume of the process chamber requiring an increase in the external dimensions, particularly if a cooling device or cooling process is employed. In addition, the increased volume increases gas residence time that can be counterproductive in a process that is not reaction rate limited, e.g., a bulk photoresist stripping process, resulting in increased processing times.
The distribution of gas across the substrate can also be improved by supplying the gas through a plurality of nozzles that extend through the ceiling or walls of the process chamber. However, process chambers having ceramic walls or ceramic ceilings are difficult to fabricate with nozzle feedthroughs extending therethrough. Ceramic walls of polycrystalline ceramic material, such as aluminum oxide or silicon, are brittle materials and it is difficult to machine feedthrough holes in these materials without breaking or otherwise damaging the ceramic. Also, other components, such as RF induction coils, which are typically located adjacent to the ceramic walls further reduce the available space for locating a gas nozzle through the ceramic walls without increasing the overall size (height) of the reactor assembly. Thus, there is a need for a process chamber having a gas distribution system that provides a uniform distribution of gas in the process chamber without requiring an excessive number of feedthroughs to be machined through chamber walls or the addition of a gas distribution mechanism and cooling hardware, if present, between the reactor gas inlet and the substrate surface.
The distribution of gas into the process chamber is also affected by the position and symmetry of the exhaust conduit, i.e., gas outlet. An axisymmetrically positioned exhaust conduit can result in asymmetric flow rates of gas across the substrate surface causing non-uniformity. Furthermore, as substrates increase in diameter to 300 mm and beyond, the corresponding increases in the volume of the process chamber and surface area of the substrate makes it even more difficult to provide a uniform distribution of process gas across the entire surface of the substrate.
Another problem arises when a portion of the gas distributor is made from metal and is located within the energized plasma sheath in the process chamber. The metal component causes localized energy perturbations that can lead to variations in plasma energy across the face of the substrate. In addition, the plasma species often chemically erode the metal to form contaminant particles that deposit upon the substrate. For example, an aluminum gas distributor is rapidly eroded by a halogen containing plasma. Thus, it is generally required for the metal portions of the gas distributor to be protected from erosion by adding a ceramic coating to the metal surface, thereby adding to the expense and complexity of the reactor assembly. In addition, the plates need to be electrically isolated from the plasma to provide a more uniform plasma distribution. This method of gas distribution can add considerable cost to the reactor in both materials and engineering time required to solve these problems.